1. Field of the Invention
The invention relates to low loss ferrites and especially to ferrites used at high, very high and ultra-high temperatures (of 1.5 MHz to 500 MHz) and more particularly materials that show low magnetic losses under high applied power values. The particular features of these materials are firstly their low sintering temperature (T less than 1000xc2x0 C.) and secondly their low magnetic losses at high, very high and ultra-high frequencies. The ferrites described in the present invention are particularly suitable for making low-loss magnetic cores for high power (100 to 1000 W) applications, very wide frequency band applications or integrated electronic applications in the radiocommunications frequency range.
2. Description of the Prior Art
The development of electronic equipment is linked to the miniaturization of the passive and active components. Among these components, the bulkiest are the passive components which fulfill the resistor, inductor and capacitor functions and, more particularly, the passive inductive or inductance components. In the xe2x80x9chigh-levelxe2x80x9d applications, which implement high electrical power values, the losses of the inductive component are determined essentially by the total losses of the magnetic material used to make the core. In the high frequency range (f greater than 1.5 MHz), nickel-zinc ferrites are used because of their appropriate magnetic properties and high electrical resistivity.
The xe2x80x9clow lossxe2x80x9d ferrites designed for high frequency applications (f greater than 1 MHz) are generally nickel-zinc ferrites with the chemical formula NixZnyFe2O4 with x+y=1. They are used as magnetic cores having a variety of forms (torus, pot, rod and other cores) enabling the making of inductors or wound transformers, the winding part being made by means of enamelled copper wire or coaxial conductors.
The performance characteristics of these components are often limited by the total losses of the ferrite which, therefore, determine the dimensions of the component and the permissible incident power.
FIG. 1 indicates the performance characteristics of a commercially available nickel-zinc ferrite optimized for applications of this type. It represents the variation of the total losses measured at 1.5 MHz as a function of the induction and at ambient temperature. The measurement is made on a wound torus using an enameled copper wire. The initial static permeability of the ferrite is equal to 125.
FIG. 2 shows the variation of the total losses of the same material as a function of the frequency and for a frequency/induction product equal to 37.5 MHz.mT, these conditions corresponding to the operation of the wideband power transformers. It must be noted that the losses diminish when the frequency is increased because the induction in the material diminishes. The total losses as a function of frequency and the induction may be estimated according to the relationship: p (f, B)=cste. Bxcex1. fxcex1 where xcex1xe2x89xa72 and xcex2xe2x89xa71. They increase monotonically when the frequency increases.
The known types of ferrites have high losses at high frequencies and at high power values.
The invention seeks to obtain ferrites that can be used to overcome this drawback.
The invention therefore relates to a ferrite material based on nickel, copper and zinc having the following formula:
NixZnyCuzCoxcex5Fe2xc2x1xcex4O4
in which:
x+y+z+xcex5=1xc2x1xcex4
xcex4xe2x89xa60.05
0.04xe2x89xa6xcex5
0.05xe2x89xa6zxe2x89xa60.35
0xe2x89xa6yxe2x89xa60.65
The invention also relates to a component applying the ferrite material, the component comprising at least one ferrite core.